Putative mutant set of the cv. Katy, a japonica rice well adapted for production in the southern U.S. Katy (PI 527707) has resistance to sheath blight disease (Rhizoctonia solani) and possesses the major blast resistance genes Pi-ta, Pi-ta2, and Pi-ks. The second subset of mutants were treated with 0.4%, 0.8% and 1.2% ethyl methane sulfonate. A total of 4880 panicles panicles were harvested from 4896 M0 and were subsequently amplified to M4 by single seed breeding method in Stuttgart, AR from 2004 to 2007. This population has been used to identify lesion mimic mutants (Jia 2005) and will be useful for the identification of useful mutants for crop improvement and functional genomics.